1. Field of the Invention
The present invention relates to a fluid cylinder mechanism. More specifically, the present invention relates to a fluid cylinder mechanism provided with a lock mechanism whereby the piston is locked in a state drawn into the cylinder.
2. Related Art
Conventionally, a fluid cylinder mechanism has been proposed in which the piston is locked in a state drawn into the cylinder (for example, refer to Japanese Unexamined Patent Application Publication No. 2009-299795).
Hereinafter, a conventional fluid cylinder mechanism 101 will be explained while referring to FIGS. 1 to 5.
The conventional fluid cylinder mechanism 101 has a sleeve 110 that is open at one end, a hollow piston rod 120, and a displacement piston rod 135.
A first chamber 114 holding operating air is formed inside the sleeve 110 by inserting a closure member 111 in the opening of the sleeve 110.
A shock-absorbing member 112 composed of urethane rubber is fixed to a ceiling surface of the sleeve 110.
A feed path 116 is formed in the sleeve 110 and the shock-absorbing member 112. Operating air is fed to the first chamber 114 via the feed path 116. A supply pipe 117 is inserted into the feed path 116 of the sleeve 110. A check valve 118 is provided at a leading end of the supply pipe 117. The escaping of operating air in the first chamber 114 to outside of the fluid cylinder mechanism 101 is avoided with this check valve 118.
The hollow piston rod 120 is configured by a cover member 127 being fit into a cylindrical body 125 having a flange portion 121, thereby forming a second chamber 126 inside. A seal member 124 is installed between a side wall of the flange portion 121 and the inside wall of the sleeve 110.
A plurality of first communication paths 133 communicating the first chamber 114 with the second chamber 126 are formed between the inner circumferential wall and the outer circumferential wall of the hollow piston rod 120.
A second communication path 134 communicating the first chamber 114 with the second chamber 126 is formed in the cover member 127 of the hollow piston rod 120. A check valve 123 is installed in the second communication path 124. This check valve 123 feeds operating air inside the first chamber 114 to the second chamber 126 by opening when the pressure of the first chamber 114 reaches a predetermined value.
An insertion hole 129 is formed in a bottom wall 128 of the hollow piston rod 120. A seat portion 141 of a ring shape is formed in the top surface of the bottom wall 128.
The displacement piston rod 135 has a disk portion 142 accommodated in the hollow piston rod 120, and a shaft portion 143 that extends from the disk portion 142. The shaft portion 143 is passed through the insertion hole 129. A bearing 131 is installed in the insertion hole 129, and serves as a seal between the insertion hole 129 and the shaft portion 143.
Packing 144 is attached to the side wall of the disk portion 142. The packing 144 slides in contact with the inside wall of the hollow piston rod 120 when the displacement piston rod 135 displaces.
When the displacement piston rod 135 is positioned at the bottom dead point in FIG. 1, the disk portion 142 is seated on the seat portion 141. As a result, a third chamber 145 is formed between the top surface of the bottom wall 128 and the disk portion 142.
A plurality of paths 146 extending along the height direction of the disk portion 142 are formed therein. The third chamber 145 and the second chamber 126 are in communication via the paths 146. The pressure of the second chamber 126 and the pressure of the third chamber 145 are, therefore, usually equal to each other.
In the conventional fluid cylinder mechanism 101 configured in the above way, the sleeve 110 is fixed at a side thereof at the shock-absorbing member 112 to the bottom surface of an upper mold 70 of a molding apparatus 50 described later, for example. On the other hand, the displacement piston rod 135 is positioned slightly above the top surface of a moveable mold 80 that moves vertically relative to the upper mold 70.
As shown in FIG. 1, the shaft portion 143 of the displacement piston rod 135 and the top surface of the moveable mold 80 are separated in an initial state.
At this time, the disk portion 142 of the displacement piston rod 135 is seated on the seat portion 141. The first chamber 114 and the second chamber 126 are in communication via the first communication paths 133, and the second chamber 126 and the third chamber 145 are in communication via the paths 146.
In this state, the first chamber 114, the second chamber 126 and the third chamber 145 are filled with operating air of a predetermined pressure.
As shown in FIG. 2, when the upper mold 70 and the moveable mold 80 operate in directions relatively approaching each other, and the shaft portion 143 of the displacement piston rod 135 immerses inwards into the hollow piston rod 120, the disk portion 142 of a displacement piston rod 135 blocks the first communication path 133.
Since there is no substantial change in the volumes of the first chamber 114, second chamber 126 and third chamber 145 at this time, the pressure of the operating air does not change.
As shown in FIG. 3, when the upper mold 70 and the moveable mold 80 further operate in directions relatively approaching each other, the hollow piston rod 120 rises relative to the sleeve 110, and the flange portion 121 rises relatively inside the sleeve 110. As a result, the height of the first chamber 114 contracts, and also a fourth chamber 147 is formed between the flange portion 121 and the closure member 111.
When the height of the first chamber 114 is contracting, the pressure of the first chamber 114 becomes higher than the pressure of the second chamber 126. If the pressure differential therebetween exceeds a predetermined value, the check valve 123 will open, and the pressure of the first chamber 114 will be bled off to the second chamber 126 and the third chamber 145, thereby eliminating the pressure differential therebetween. When the pressure differential has been eliminated, the check valve 123 closes.
The pressure of the first chamber 114 and the pressures of the second chamber 126 and the third chamber 145 gradually rise while assuming a substantially equal state, by repeating this operation.
As shown in FIG. 4, the upper mold 70 and the moveable mold 80 further operate in directions relatively approaching each other until the top surface of the flange portion 121 of the hollow piston rod 120 rises to a position (ascent limit position) substantially contacting the shock-absorbing member 112 of the sleeve 110.
At this time, the pressures of the first chamber 114 and the feed path 116 and the pressures of the second chamber 126 and the third chamber 145 are substantially equal, and in an extraordinarily high pressure state. The pressure of the fourth chamber 147 is nearly atmospheric pressure.
As shown in FIG. 5, when the upper mold 70 and the moveable mold 80 operate in directions relatively separating from each other from the state shown in FIG. 4, the force supporting the hollow piston rod 120 from below is lost. As a result, the hollow piston rod 120 descends relative to the sleeve 110.
Then, the pressure depressing the hollow piston rod 120 downward reduces, since the pressure of the first chamber 114 declines due to the hollow piston rod 120 descending. On the other hand, the pressure supporting the hollow piston rod 120 from below increases, since the pressure of the fourth chamber 147 rises due to the hollow piston rod 120 descending.
The hollow piston rod 120 is supported by the pressure of the fourth chamber 147, and enters a locking state at a position at which the pressure of the fourth chamber 147 supporting the hollow piston rod 120 from below and the weight of the hollow piston rod 120 itself are balanced, and does not descend more than this.